Multiple types of voltage-gated K+ (Kv) channels with distinct time- and voltage-dependent properties and pharmacological sensitivities have been identified in the mammalian myocardium. This diversity has a physiological significance in that the various Kv channels play distinct roles in controlling action potential waveforms and refractoriness. Although considerable progress has been made in identifying the Kv channel pore-forming (?) subunits that encode diverse cardiac Kv channels, the functional roles of the Kv channel accessory subunits (minK/ MiRPs, Kv?, KChAP, KChIP, DPPX) are rather poorly understood. Studies in heterologous expression systems suggest that Kv accessory subunits can modulate the properties of a variety of Kv ? subunit encoded channels and that each type of Kv channel likely is modulated by multiple accessory subunits. Other recent studies suggest that cardiac Kv (and other) channels function as components of macromolecular protein complexes, comprising pore-forming and accessory subunits, as well as additional regulatory proteins that influence channel properties and mediate interactions with the actin cytoskeleton and the extracellular matrix. To define the physiological roles of the Kv?1, KChlP2 and DPP6 subunits, the studies proposed here will probe directly the functioning of these subunits in the generation of the native Kv channels, lto,f, Ito.s, IK,slow and Iss, in intact cardiac (mouse ventricular) myocytes. The expression levels or the properties of the accessory subunits will be manipulated in vivo and in vitro, and the functional consequences of these manipulations on the properties and cell surface expression of myocardial lto,f, Ito.s, IK,slow and Iss will be determined directly (and simultaneously). The proposed studies will reveal whether individual Kv channel types are regulated/modulated by multiple Kv accessory subunits. In addition, these studies will allow direct testing of the hypothesis that Kv accessory subunits are multifunctional, regulating/modulating the functioning of multiple types of (Kv a subunit encoded) cardiac Kv channels. We anticipate that these studies will provide fundamentally important new insights into the role of Kv channel accessory subunits in the dynamic regulation of cardiac Kv channel macromolecular complexes.